1. Field of the Invention
The present disclosure relates to a fuel cell system and a method for stopping an operation of the fuel cell system.
2. Discussion of the Background
A fuel cell supplies a fuel gas (gas essentially containing hydrogen, e.g., hydrogen gas) to an anode electrode, and supplies an oxidant gas (gas essentially containing oxygen, e.g., air) to a cathode electrode to cause an electrochemical reaction of the gases, which provides DC current energy.
A solid polymer electrolyte fuel cell, for example, is known as one kind of fuel cell. The solid polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) having an anode electrode and a cathode electrode provided on the respective sides of an electrolyte membrane formed by a polymer ion exchange membrane, and supported by a pair of separators. A fuel gas passage for supplying the fuel gas to the anode electrode is formed between one of the separators and the MEA, and an oxidant gas passage for supplying the oxidant gas to the cathode electrode is formed between the other separator and the MEA.
At the time the fuel cell is stopped, the supply of the fuel gas and the oxidant gas is stopped, but the fuel gas remains in the fuel gas passage in the fuel cell and the oxidant gas remains in the oxidant gas passage in the fuel cell. Accordingly, when the halt period of the fuel cell is long, in particular, the remaining fuel gas and oxidant gas may penetrate the electrolyte membrane to impair the electrode catalyst and the catalyst support, thus shortening the service life of the fuel cell.
To cope with the shortcoming, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2007-506243 discloses a technique such that a fuel cell system is provided with a combustor which causes hydrogen (fuel gas) to react with air (oxidant gas), and at the time of stopping the fuel cell, oxygen-consumed air (nitrogen gas) from the combustor is supplied to the cathode (oxidant gas passage) and the anode (fuel gas passage).
However, the fuel cell system disclosed in this publication needs the combustor, a valve (fuel inactivation valve) for supplying the fuel gas to the combustor, etc., complicating the system.
It is also known that when an anode gas is switched to a hydrogen gas from a nitrogen gas upon activation of a fuel cell, the cathode side partially comes to a high-potential state (see, for example, “New Development On Research On Batteries/Fuel Cells—Aiming At Achieving Low-Carbon Society—Efforts To Overcoming The Problems Of Approaching Practical Application Of Solid Polymer Electrolyte Fuel Cells”, by Kazumi Tanimoto and Isao Nagai, AIST TODAY, Aug. 1, 2009, Vol. 9, No. 8, p. 12-13).